Coating composition for protecting metal surfaces from corrosion



Patented Sept. 1 1.1951

UNITED STATES PATENT OFFICE COATING COMPOSITION FOR PROTECTING METALSURFACES FROM CORROSION Charles T. Watson, Bessemer, Ala., assignor toTennessee Coal, Iron and Railroad Company,-

a corporation of Alabama No Drawing. Application April 20, 1949, SerialNo. 88,686

Atmospheric corrosion of metal and particularly metal structural membersexposed to the weather, is a perennial problem and numerous efforts havebeen made to provide a universally applicable protective coatingtherefor. So far as I am aware, however, no wholly satisfactoryprotective coating has become available. to supply this need, I haveinvented a'novel paint having superior qualities of durability,adherence and protection against chemical action of any kind on theunderlying metal.

The improved paint composition of my invention comprises awater-insoluble film-formin liquid vehicle carrying in suspension alarge proportion, i. e., from one-third to one-half, of solids includingphosphoric acid or metal salts thereof and preferably inert material inthe nature of a pigment, filler or extender. For best results, the paintshould be baked after application. The vehicle may be any of thosecommonly employed in the manufacture of paint, enamel or lacquer,specifically linseed oil, either alone or thinned with turpentine,or'synthetic resin such as a phenolformaldehyde condensation product, inlinseed oil or other organic compound, e. g., amyl acetate. Thesuspended solids may include the phosphate of iron, manganese or zinc ora mixture of these phosphates. More specifically, the metal phosphatemay be the secondary or tertiary phosphate of iron, manganese or zinc,as well as the primary phosphate, or a mixture of the several phosphatesof one metal or more than one. I may also use phosphoric acid inaddition to metal salts thereof. The pigment may be ground slate,

lampblack or other such material or a mixturethereof. The filler may bea metal oxide such as zinc or titanium oxide, or a mixture of two ormore such oxides.

The proportion of solid material to vehicle may vary over a considerablerange, 1. e., between a ratio of one to one and a ratio of one partsolid material to two parts vehicle by weight. If the solids content bereduced below V by weight, the durability of the coating is impairedwhereas if In order 1 Claim. (Cl. 108-14) 2 the solids exceed V theconsistency is such as to interfere with easy brushing or spraying. Thepaint is applied to the surface to be protected in any convenientmanner, i.' e., as by spraying, brushing or dipping and the resultingcoating is preferably baked for about 10 minutes at a temperaturebetween 350 and 400 F.

In accordance with my invention, very good protecting qualities areobtained when mixtures of secondary and tertiary phosphates of iron,

manganese, and zinc are used. Under equilibrium conditions secondaryphosphates tend to decompose into mixtures of phosphoric acid, primaryphosphates, secondary phosphates and tertiary phosphates which, in thepresence of heat, react with phosphate-coated surfaces and facilitatecoatings of high adhesion and low porosity. Primary phosphates react ina similar manner after decomposing into mixtures of phosphoric acid.

primary phosphates, secondary phosphates and tertiary phosphates. Goodprotective qualities are obtained, howeve whenonly tertiary phosphatesare employed in paints applied over certain phosphate coatings.

The solid material suspended in the vehicle may consist of from 15 to40% phosphate and from 15 to 40% zinc oxide both by weight, the balancebeing made up of pigment or other flller. Preferably the phosphate andoxide should each comprise at least 25% by weight of the total solids.With less than- 15% of these compounds the desired protection is notassured. The use of more than 40% does not materially increase theprotection afforded.

The invention may be more fully understood from a consideration of the.following illustrative examples, all of which are designed primarily foruse on zinc which previously has been given a phosphate treatment. Thepercentages in each example are by weight, as are the indicated numberof parts.- v

ExAMPLE I Three parts pigment I Per cent Tertiary zinc phosphate 40 Zincoxide 40 Titanium oxide 20 Total Four parts vehicle Per cent Linseed oil'10 Turpentine 30 Total 100 3 4 EXAMPLE It Five Wt: vehicle Percent tPer cent "Bakelite" 60 Tertiary zinc phosphate 40 Amy] Meta Zinc oxide40 Titanium oxide 2o Total 100 EXAMPLE VII Two parts vehicle one M W Percent rerun 85 Phoslpohate compound containing: Amy is 4 V 45 1 acetatezn 1m [5 Mn 10 Total F8 12 EXAMPLE 111 other 13 V Four parts pigmentTotal phosphates 30 p ceni; Zinc oxide :5 Tertiary zinc phosphate 25SW59 Zinc oxide 25 Bmablack 1s slate Titanium oxide 5 Lampbiack 15Titanium nxidn 5 Total 100 25 Total 100 One Part vehicle t hick PercentFive m 8 1 Per cent 2 Linseed on 100 Bake Total 100 EXAMPLE IV EXAMPLEV111 Four parts pigment a One part pigment Per cent Per cent Tertiaryzinc phosphate 25 Phosphate compound containing: Zinc oxide 25 P04 45Slate 30 Zn 15 Lampblack 15 4o Mn 10 Titanium oxide 5 Fe 12 Other 18Total 100 Total phosphates 3o Zinc oxide 25 Five parts we .icle 45 slate25 P r cent Lampblack 1s "Bakelite Titanium oxide 5 Amyl aceta 10 ITotal 100 Total 60 EXAMPLE v W 50 Per Four parts pigment n a l on Percent m me 50 Tertiary zinc phosphate 25 so Phosphoric acid 5 Zinc oxide25 Ferric oxide 50 v Total 100 Total 100 x mm 1x Five parts vehicle Twoparts pigment Percent Tertiary zinc phosphate 25- Linseed oi Secondaryzinc phosphate 1o Turpentine 5 Zinc oxide 35 05 Titanium oxide 10 Totallien-1c oxide 30 mm V! Total 100 Three part: pigment cent 70 Three partsvehicle Tertiary zinc phosphate 25 Percent Zinc oxide 25 "Bakelite" ooFerric oxide 50 Amyl acetate 10 Total 100 10 Total no In all cases, thecoating is applied by brushing, dipping or spraying and is preferablybaked at 350 or 400 F. for about ten minutes.

The specific method of producing the ground coating of phosphate overwhich my improved coating is applied forms no part of the invention. Anysuitable method may be employed. Where the surface to be protected is azinc surface such as a galvanized coating, for example, it may betreated by contacting it with a, phosphoric acid solution containingphosphates of iron. manganese and zinc, as described and claimed in myco-pending application Serial No. 72,751; filed January 25, 1949, whichissued on July 10, 1951 as Patent No. 2,559,812 for Solution and Methodfor Coating Zinc Surfaces." Other methods of producing the initialphosphate coating may be employed, however, as will readily beunderstood by those skilled in the art.

The improved coatings produced in accordance with my invention arehighly resistant to atmospheric and other types oi! corrosion, andpossess qualities of good adherence and appearance.

I claim:

A protective paint for metal surfaces comprising from to solids byweight suspended in a water insoluble film-forming vehicle, said solidsconsisting of from 15 to 40% by weight of a phosphate of a metal fromthe group consisting of iron, manganese and zinc, and substantially thebalance inert filler.

CHARLES T. WATSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,081,160 Tanner May 25, 19372,148,862 Kern Feb. 28, 1939 2,184,324 Straus Dec. 26, 1939 2,227,928Drucker Jan. '7, 1941 2,385,800 Douty et a1. Oct. 2, 1945

